A study by Bell (A-45) investigated the hypothesis that alteration of the vitamin D–endocrine system in blacks results from reduction in serum 25-hydroxyvitamin D and that the alteration is reversed by oral treatment with 25-hydroxyvitamin D3. The eight subjects (three men and five women) were studied while on no treatment (control) and after having been given 25-hydroxyvitamin D3 for 7 days

(25-OHD3). The following are the urinary calcium (mg/d) determinations for the eight subjects under the two conditions.
Subject Control 25-OHD3 A 66 98 B 115 142 C 54 78 D 88 101 E 82 134 F 115 158 G 176 219 H 46 60 Source: Data provided courtesy of Dr. Norman H. Bell.